Melatonin Onset Timing Calculator

About this calculator

Your body's internal clock releases melatonin naturally in the evening, and the point where blood levels first rise noticeably in dim light — called the Dim Light Melatonin Onset (DLMO) — is the gold-standard marker chronobiologists use to pinpoint your circadian phase. DLMO typically falls around two hours before your habitual bedtime, though it varies from person to person.

Taking a melatonin supplement works differently depending on your goal. To simply help you fall asleep, a dose taken 30–60 minutes before bed is standard practice. To shift your circadian clock earlier — useful for jet lag after flying east, or for delayed sleep phase syndrome — chronobiology research instead recommends a small dose taken several hours before your natural DLMO, since melatonin acts as a phase-shifting signal to the clock itself, not just a sedative, and timing it wrong can shift your rhythm the wrong direction.

This calculator estimates your DLMO from your bedtime and then suggests a melatonin timing window suited to whichever goal you select, sleep onset or phase advance.